Semiconductor devices are strongly desired to be further reduced in size as flash memories as storage devices now have a larger capacity and markets of, for example, image sensors for high resolution cameras of mobile phones and smartphones are expanded. For producing various electronic devices, photolithography is widely used. Photolithography has contributed to the size reduction of semiconductor devices by using light sources of light having a shorter wavelength. In the case where a KrF excimer laser or any other laser that emits light of a shorter wavelength is used as a light source, a chemical amplification resist is generally used. A commonly used chemical amplification resist is a solution containing a functional resin as a main component, a photoacid generator, and several types of additives. It is important that the functional resin as the main component should have characteristics such as etching resistance, adherence to a substrate, transparency to light from the light source to be used, development rate and the like in a good balance. Such characteristics of the functional resin determine the resist performance.
The functional resin used for a photoresist for a KrF excimer laser is generally a polymer containing a vinyl compound, an acrylate or the like as a repeat unit. A functional resin proposed for a resist for KrF excimer laser lithography is a hydroxystyrene-based resin (Patent Document 1). A functional resin proposed for a resist for ArF excimer laser lithography is an acrylic resin containing an adamantyl(meth)acrylate as a basic backbone (Patent Documents 2 through 6). The basic backbone of the functional resin is now being defined. However, a functional resin is not used in the state of containing a single repeat unit. A reason for this is that a resin containing a single repeat unit does not fulfill all the necessary characteristics including the etching resistance and the like. In actuality, a functional resin is formed of a copolymer containing a plurality of, namely, two or more, repeat units including functional groups each for improving a characteristic, and the functional resin is combined with a photoacid generator or the like and dissolved in a solvent to form a photosensitive resin composition to be used.
Recently, size reduction is advanced with the lithography process. ArF excimer laser lithography is advanced and now uses liquid immersion exposure and even double patterning exposure. In addition, lithography using extreme ultraviolet (EUV) light, which is a target of attention as a next-generation lithography technology, and electron beam direct drawing, have been developed in various manners.
Although various developments have been made for the purpose of further size reduction, the influence of contrast deterioration caused by diffusion of acid that is generated from a photoacid generator after the exposure has become more serious as the width of the circuit is decreased. Methods for controlling the acid diffusion now proposed include a method of enlarging the structure of the photoacid generator (Non-patent Document 1) and a method of using a resin containing a monomer that contains a photoacid generator (Patent Document 7, Non-patent Document 2). Another method now proposed is a method of extending a pendant part of a resist polymer to block an acid diffusion path (Patent Documents 8 and 9).
With the double patterning exposure technology, an LLE (litho-litho-etch) process is now being studied. According to the LLE process, a first pattern is formed of a first resist material, then a pattern is formed of a second resist material while the first resist pattern is maintained, and the two patterns are subjected to dry etching at the same time. In this process, the patterns are made insoluble by a crosslinking reaction that is caused by heating. If the glass transition temperature of the first resist material is low, a flow of the pattern is generated, which is not preferable.
In such a situation, Patent Documents 11 and 12 propose a photoresist polymer having an amide bond and an adamantane structure but provide no example in which such a photoresist polymer is actually produced. It has not been known whether such a photoresist polymer is actually usable.